I do NOT recommend hot tank blue as a DIY project, and certainly not for one or a few guns. The cost has already been mentioned, but also it is VERY DANGEROUS. You are fooling with caustic salts at a high temperature. One splash can burn through to the bone before you can even think about it. You need protective gear like a heavy rubber apron and boots, goggles, gloves, a heavy cap and face shield. And a lab type douse shower that will dump gallons of water in seconds. And a place for that water to go.

Hot tank bluing in your kitchen? Some people claim they do it and it is easy. I hate to call folks liars, but they are certainly either misleading others or taking great risks with their own safety (or they literally don't know what they are talking about).